Let’s face it, as human beings we’re terrible at estimating how long a project will take to complete (even Elon Musk has been off by YEARS in his predictions for SpaceX!)
𝗪𝗛𝗬? Two reasons:
❌ We’re simply too optimistic and assume everything will go well.
❌ Calculating a single completion time does not FORCE us to consider alternate scenarios.
Once THE DATE been communicated, everyone tends to remember THE DATE – and NOT the underlying ASSUMPTIONS behind it, no matter how carefully they're stated.
A variation of PERT analysis; PERT stands for 𝘗𝘳𝘰𝘨𝘳𝘢𝘮 𝘌𝘷𝘢𝘭𝘶𝘢𝘵𝘪𝘰𝘯 𝘢𝘯𝘥 𝘙𝘦𝘷𝘪𝘦𝘸 𝘛𝘦𝘤𝘩𝘯𝘪𝘲𝘶𝘦. Even though it was first used by the US Navy in the 50’s for the development of the Polaris submarine-launched nuclear missile, it’s not rocket science:
In PERT, for each project task we calculate 3 durations:
👉 Optimistic (O): min. time to accomplish (best-case scenario)
👉 Pessimistic (P): max. time to accomplish (worse-case scenario)
👉 Most Likely (M): best current estimate to accomplish
A project plan for each of the three scenarios can then be developed and analyzed in MS Project, Excel, etc. to determine a RANGE of project durations and completion dates.
𝐁𝐄𝐍𝐄𝐅𝐈𝐓𝐒 𝐨𝐟 𝐏𝐄𝐑𝐓 𝐢𝐧𝐜𝐥𝐮𝐝𝐞:
✅ A series of realistic scenarios for our project based on what can go right AND what can go WRONG!
✅ NOT being tied down to a single (uncertain) date, since the output is a RANGE of completion times.
✅ An estimate of the VARIABILITY in our project timeline.
Even IF a completion date cannot be moved (say due to an audit or regulatory deadline), the three estimates can be used to calculate project duration with:
🔹 Additional resources (Optimistic)
🔹 Current resources (Most Likely)
🔹 Less resources (Pessimistic)
Which can help us figure out whether we’ll need additional people, machines, material, etc. to meet our deadline.
We would NOT make an important decision based on a sample of n = 1 if we could avoid it, so why base your project timeline on a single estimate?
Give PERT analysis a try when scheduling your next project.
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